The present invention relates to dual filters having a full flow filter element and a bypass filter element. More particularly, the present invention relates to a dual filter having a full flow filter element and a bypass filter element arranged in tandem with auxiliary structure which enhance filtering function.
Filter cartridges used for filtering fluids such as lubricating oil can be arranged with a full flow filter element and a bypass filter element, the bypass filter element being stacked on the full flow filter element with the fluid flowing radially through the filter elements into hollow cores thereof and then axially out of the canister.
This arrangement is widely employed to filter lubricating oil used in internal combustion engines. Engine wear, specifically piston ring wear, is directly related to the amount of actual filtration of lubricating oil by both full flow and bypass filters which is mixed after filtration. It has been found that by combining filtration provided by a full flow filter element with that of a bypass filter element substantially reduces engine wear as compared to using only full flow filtration. Moreover, by using a combination of full flow and bypass flow lubricating oil, service intervals can be increased so that maintenance expense is reduced. Maintenance expense is a major consideration in the total expense of operating a vehicle. This is, of course, a major concern for fleets of vehicles, such as the fleets operated by trucking companies. In addition, by keeping lubricating oil clean, it can remain in engines longer and does not have to be recycled at shorter intervals. Consequently, environmental concerns due to vast amounts of used lubricating oil are reduced because less used oil must be recycled. It is therefore beneficial to enhance the performance of lubricating oil cartridges which utilize both full flow filter elements and bypass filter elements.
In view of the aforementioned considerations, it is a feature of the present invention to provide a filter for removing particles from a fluid wherein the filter comprises a canister having a first end with radially disposed inlet openings and a central outlet opening and having a second end which is closed. A first filter element having a small particle annular filter media defining a first substantially cylindrical hollow core is disposed adjacent the first end of the canister. A second filter element having a sludge removing annular filter media defining a second substantially cylindrical hollow core is stacked axially with respect to the first filter element. A flow mixing element connects the second hollow core to the first hollow core and includes a flow deflector which imparts a rotational component to the fluid as the fluid flows axially from the first hollow core to the second hollow core. Consequently, fluid flowing radially through the small particle filter media mixes with the rotating fluid which has been filtered by the second filter media before passing through the central outlet opening of the filter canister. The capacity of the filter is increased by providing an array of angled fins which impart rotation to the fluid around the filter elements after the fluid enters the canister and flows toward the second end of the canister.
In another aspect of the invention, the flow mixing element comprises an annular channel formed about a core, the annular channel having a flow deflector therein, which in a more specific aspect of the invention comprises at least one axially-extending angularly displaced rib.
In a further aspect of the invention, the afore-described rib extends across the annular channel and supports the core of the mixing element therein. In a more specific aspect, the core has at least one end which is closed to the passage of fluid so that the fluid flows from the second hollow core to the first hollow core only through the annular channel.
In still further aspects of the invention, the filter is arranged with the first filter element disposed above the second filter element and with a chamber within the canister below the second filter element for accumulating particles separated from the fluid by centrifugal force to keep those particles out of the filter elements.
In a specific embodiment, the aforedescribed filter is used to filter lubricating oil for internal combustion engines.